U.S. patent application number 14/256919 was filed with the patent office on 2014-08-14 for triple-tier anycast addressing.
The applicant listed for this patent is Cisco Technology, Inc.. Invention is credited to Thomas Edsall, Dino Farinacci.
Application Number | 20140226669 14/256919 |
Document ID | / |
Family ID | 39676100 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140226669 |
Kind Code |
A1 |
Farinacci; Dino ; et
al. |
August 14, 2014 |
TRIPLE-TIER ANYCAST ADDRESSING
Abstract
In one embodiment, a solution is provided wherein redundant
routers are treated as a single emulated switch. When a packet is
received at a layer 2 edge switch from a host, the layer 2 edge
switch may determine a switch identifier for the emulated switch
using a destination anycast hardware address contained in the
packet. The anycast hardware address may identify an emulated
switch comprising a plurality of routers. Then a header may be
added to the packet, the header including the switch identifier.
Following that, the packet may be forwarded to another layer 2
switch along a shortest path from the layer 2 edge switch to the
emulated switch.
Inventors: |
Farinacci; Dino; (San Jose,
CA) ; Edsall; Thomas; (Cupertino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cisco Technology, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
39676100 |
Appl. No.: |
14/256919 |
Filed: |
April 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13584546 |
Aug 13, 2012 |
8743738 |
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14256919 |
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Current U.S.
Class: |
370/392 ;
370/401 |
Current CPC
Class: |
H04L 49/70 20130101;
H04L 61/6022 20130101; H04L 49/604 20130101; H04L 61/103 20130101;
H04L 45/58 20130101; H04L 45/00 20130101; H04L 61/6077 20130101;
H04L 49/552 20130101; H04L 49/351 20130101; H04L 12/4633 20130101;
H04L 45/74 20130101 |
Class at
Publication: |
370/392 ;
370/401 |
International
Class: |
H04L 12/741 20060101
H04L012/741 |
Claims
1. An apparatus, comprising: a processor; and a memory, at least
one of the processor or the memory being adapted for: receiving a
packet by an edge switch, wherein the packet includes an anycast
address that corresponds to a same address that is assigned to each
of a plurality of routers of an emulated switch, the network
including a plurality of switches; adding a header to the packet;
and forwarding the packet from the edge switch to another
switch.
2. The apparatus of claim 1, at least one of the processor or the
memory being adapted for performing steps, further comprising:
determining a switch identifier for the emulated switch using the
anycast address; wherein the header includes the switch
identifier
3. The apparatus of claim 2, wherein the determining comprises
looking up the anycast address in a table to retrieve the switch
identifier.
4. The apparatus of claim 1, wherein forwarding comprises
forwarding the packet to another switch along a shortest path from
the edge switch to the emulated switch.
5. The apparatus of claim 4, at least one of the processor or the
memory being further adapted for performing steps, comprising:
determining the shortest path.
6. The apparatus of claim 4, wherein the shortest path is a
shortest operative path from the edge switch to the emulated
switch.
7. The apparatus of claim 4, wherein the shortest path is
determined based on a source address of the packet, using a hash
table, if the shortest path cannot be determined based on distance
due to a tie between two or more paths.
8. The apparatus of claim 1, wherein the same address is a Media
Access Controller (MAC) address, wherein the anycast address
corresponds to the same MAC address that is assigned to each of the
routers of the emulated switch.
9. The apparatus of claim 1, wherein the routers do not run a hot
standby routing protocol.
10. The apparatus of claim 1, wherein the network including the
plurality of switches is a Data Center Ethernet (DCE) network.
11. An apparatus, comprising: a processor; and a memory, at least
one of the processor or the memory being adapted for: transmitting
an address request to an emulated switch including a plurality of
routers, wherein each of the plurality of routers of the emulated
switch is assigned a same address; and receiving an address reply
from the emulated switch, the address reply including an anycast
address shared between each router in the emulated switch, wherein
the anycast address corresponds to the same address that is
assigned to each of the routers of the emulated switch.
12. The apparatus of claim 11, wherein transmitting an address
request to an emulated switch comprises transmitting the address
request to a first one of the plurality of routers of the emulated
switch, and wherein receiving an address reply from the emulated
switch comprises receiving the address reply from the first router,
the address reply including an anycast address shared between each
router in the emulated switch.
13. The apparatus of claim 12, wherein the network device has an
interface with the first one of the plurality of routers of the
emulated switch.
14. The apparatus of claim 11, wherein the network device has an
interface with at least one of the plurality of routers of the
emulated switch.
15. A method, comprising: transmitting an address request to an
emulated switch including a plurality of routers, wherein each of
the plurality of routers of the emulated switch is assigned a same
address; and receiving an address reply from the emulated switch,
the address reply including an anycast address shared between each
router in the emulated switch, wherein the anycast address
corresponds to the same address that is assigned to each of the
routers of the emulated switch.
16. A method, comprising: receiving a packet by a layer 2 edge
switch, wherein the packet includes an anycast address that
corresponds to a same address that is assigned to each of a
plurality of routers of an emulated switch, the network including a
plurality of layer 2 switches; adding a header to the packet; and
forwarding the packet from the layer 2 edge switch to another layer
2 switch.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 13/584,546 filed Aug. 13, 2012, and
this application also claims priority from U.S. patent application
Ser. No. 11/670,544 filed on Feb. 2, 2007, and both of the
aforementioned applications are hereby incorporated by reference
for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to computer networking.
[0004] 2. Description of the Related Art
[0005] Data management within organizations is an ever increasing
concern, especially with the rise of the Internet information age.
The heart of this data management function is sometimes known as a
data center. Over the last decade, data centers have evolved into
the strategic focus of Information Technology (IT) efforts to
protect, optimize, and grow the organization.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates an "isolated application"
environment.
[0007] FIG. 2 illustrates a DCE network.
[0008] FIG. 3 illustrates an example network containing layer 2
switches coupled to an emulated switch.
[0009] FIG. 4 illustrates an example of an ARP request packet.
[0010] FIG. 5 illustrates an example of an ARP request packet with
an appended MAC-in-MAC header.
[0011] FIG. 6 illustrates an example of an ARP reply packet with an
appended MAC-in-MAC header.
[0012] FIG. 7 illustrates an example method for handling a hardware
address request to a router in an emulated switch of two or more
routers.
[0013] FIG. 8 illustrates an example method for handling a packet
received at a layer 2 edge switch from a router in an emulated
switch of two or more routers.
[0014] FIG. 9 illustrates an example method for handling a packet
from a host at an edge switch in a network containing layer 2
switches.
[0015] FIG. 10 illustrates an example method for handling a packet
from a host at an edge switch in a network containing layer 2
switches.
[0016] FIG. 11 illustrates an example apparatus for handling a
hardware address request to a router in an emulated switch of two
or more routers.
[0017] FIG. 12 illustrates an example apparatus for handling a
packet received at a layer 2 edge switch from a router in an
emulated switch of two or more routers.
[0018] FIG. 13 illustrates an example apparatus for handling a
packet from a host at an edge switch in a network containing layer
2 switches.
[0019] FIG. 14 illustrates an example apparatus for handling a
packet from a host at an edge switch in a network containing layer
2 switches.
[0020] FIG. 15 illustrates a simplified architecture of DCE
switch.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
[0021] In one embodiment, a solution is provided wherein redundant
routers are treated as a single emulated switch. When a packet is
received at a layer 2 edge switch from a host, the layer 2 edge
switch may determine a switch identifier for the emulated switch
using a destination anycast hardware address contained in the
packet. The anycast hardware address may identify an emulated
switch comprising a plurality of routers. Then a header may be
added to the packet, the header including the switch identifier.
Following that, the packet may be forwarded to another layer 2
switch along a shortest path from the layer 2 edge switch to the
emulated switch.
Example Embodiments
[0022] In this application, numerous specific details are set forth
in order to provide a thorough understanding of the present
invention. It will be obvious, however, to one skilled in the art,
that the present invention may be practiced without some or all of
these specific details. In other instances, well known process
steps have not been described in detail in order to not obscure the
present invention.
[0023] Data center managers face several challenges in fulfilling
the goals of data centers. Most enterprise data centers grew
rapidly to meet the explosive economic growth of recent times.
Consequently, applications commonly stand alone in underutilized,
isolated infrastructure silos. Each infrastructure silo is designed
based on the inclination of the specific application being
deployed, so that a typical data center supports a broad assortment
of operating systems, computing platforms, and storage systems. The
disparate infrastructures supporting different application
"islands" are difficult to change or expand and expensive to
manage, integrate, secure, and back up. FIG. 1 illustrates an
"isolated application" environment.
[0024] One solution to this problem is to design a data center
environment that is highly scalable, resilient, secure, and able to
integrate multiple applications and protocols. One such solution is
known as the Data Center Network Architecture. A specific
implementation of the Data Center Network Architecture is known as
Data Center Ethernet (DCE). DCE allows for consolidation of input
and output, and improved forwarding of communications within the
network. This may be accomplished via specialized protocols and
functionality operated by switches within a DCE network via network
layer 2. Each of the switches within the DCE network may be a layer
2 device. FIG. 2 illustrates a DCE network. Edge switch 200 may be
connected to a host 202. Edge switch 204 may be connected to host
206. Edge switches 200, 204 may then be connected to several core
switches 208, 210, which then may be connected to other edge
switches 212, 214. Each DCE switch may be assigned a unique
identifier. A routing protocol, such as
Intermediate-System-to-Intermediate-System (IS-IS), may be used
inside DCE. Edge switches implementing this routing protocol may
append information to packets sent though the DCE. This appended
information may be in the form of a MAC-in-MAC header attached to
the packet. Edge switches 212, 214 may then each be connected to
layer 3 devices, such as routers 216, 218. Rather than forwarding
packets to MAC addresses, DCE switches send packets to edge
switches based on the edge switch identification via the MAC-in-MAC
header. The edge switch then knows which of its ports to send the
packet out to arrive at the correct IP address (for example, the
port connected to router 216), and strips off the MAC-in-MAC header
prior to doing so.
[0025] Rather than operate routers 216 and 218 independently, it is
often beneficial to link the routers so that one router can act as
a backup to the other router in case of router or link failure.
This linking may be accomplished via another routing protocol, such
as Hot Standby Routing Protocol (HSRP). Other hot standby routing
protocols include Virtual Router Redundancy Protocol (VRRP) and
Gateway Load Balancing Protocol (GLBP). In these protocols, several
routers are connected to the same subnet of a network and work
together to present the appearance of a single virtual router.
Typically, a single virtual IP address is assigned to the routers,
which the links to a single virtual MAC address. The single virtual
MAC address, however, points to a particular one of the routers,
designated as the "active" router, whereas the other router(s) are
designated as "backup." If one router goes down, another takes over
and the virtual MAC address is mapped to the backup router.
However, while both are running, only one is being used for
outbound communications. This can be inefficient for several
reasons.
[0026] First of all, using just one of a plurality of redundant
routers as the active router for outbound communications can create
a bottleneck at the single router or on one of its associated
links. It would be much more efficient to load balance between the
redundant routers. Second of all, even if a hot routing protocol is
utilized to load balance between redundant routers, the traffic
generated by these protocols can be wasteful. Third of all, the
amount of time for a router to switch from active to backup is
non-trivial. If faster convergence is desired, a different solution
is required.
[0027] A solution is provided wherein the redundant routers are
treated as a single emulated switch. This allows for both a failure
recovery and a load-balancing mechanism for host-switch-router
connectivity through a protocol, such as DCE, used in network
containing layer 2 switches. Through the use of this solution, hot
standby routing protocols such as HSRP, VRRP, and GLBP can be
eliminated.
[0028] Configuration of the network may be accomplished by first
assigning the same IP address to all routers in the emulated
switch. This IP address may be known as the "router anycast
address." Additionally, the same MAC address may be assigned to all
routers in the emulated switch. This MAC address may be known as a
"router anycast MAC address." Each host may then be configured with
a default router using a virtual IP address. The virtual IP address
maps to a virtual MAC address. The virtual MAC addresses for the
routers in the virtual switch correspond to a single anycast
hardware address. The anycast hardware address may be used as a
switch identification. This switch identification may be advertised
to all layer 2 switches within the network using a protocol such as
IS-IS, RIP, or (EIGRP) as long as the edge switches have a
reachable connection to the router.
[0029] FIG. 3 illustrates an example network containing layer 2
switches coupled to an emulated switch. When a packet is to be sent
from a host 300 to a network, such as the Internet, coupled to the
emulated switch 302, it may forward the packet to the closest edge
switch 304. However, this host 300 does not have a MAC address of a
default router in its memory, such as an address resolution
protocol (ARP) cache. Therefore, the host 300 may first send a
request for the router anycast address as, for example, an ARP
request. The ARP request is a broadcast packet that is transmitted
across the DCE network on the broadcast tree. Since the set of
routers is part of an emulated anycast switch, only one link into
the emulated anycast switch receives the ARP request. This may be
accomplished by, for example, coordination between edge switches
connected to a particular emulated switch. The link on which the
request is sent is connected to a single router, despite the fact
that the router may be a part of an emulated switch.
[0030] The router that receives the ARP request may ARP reply by
sending a unicast packet to the ARP requesting host. This allows
the first-hop switch, directly connected to the host, to know the
edge switch associated with the router. This edge switch may be
identified according to the switch identification associated with
the emulated anycast switch. The ARP reply may be sent with the
source MAC address equal to the router anycast MAC address so that
the edge switches, directly connected to the hosts, associate the
MAC address with the emulated anycast switch.
[0031] At this point the host's off subnet traffic will find the
shortest path to the emulated anycast switch. This may or may not
be the same router that replied to the ARP request. For example,
while router 306 may have responded to the ARP request, the path to
router 308 may actually be the shortest path for traffic. Other
hosts will find their own shortest paths to the emulated anycast
switch, which may be through a different router. This effectively
load balances between the redundant routers in the emulated switch.
Additionally, if the connection to a particular router goes down,
either by a topology change in the network or the router itself
goes down, traffic is quickly rerouted to other routers. This is
because a protocol, such as DCE, used in a network containing layer
2 switches, can discover topology changes or downed links much
faster than a hot standby routing protocol such as HSRP, VRRP or
GLBP. A solution is provided that takes advantage of this fact to
perform failover much quicker than prior art solutions since
failover can now be performed by the network of switches
itself.
[0032] Assume host A 300 wants to discover a MAC address for one of
the routers 306, 308. It may transmit the ARP packet depicted in
FIG. 4. The IP source address 400 may be the IP address of A. The
IP destination address 402 may be the anycast IP address of SW7.
The Layer 2 destination address 404 of the packet may be set to
broadcast (all addresses). The layer 2 source address 406 may be
Host-A 406.
[0033] Upon receipt of the ARP packet from Host A 302, switch SW1
304 learns Host A 300 is off a particular interface (for example,
interface 2). It may then append the MAC-in-MAC header depicted in
FIG. 5. Here, the destination 500 may be set to broadcast, since
the packet is still an ARP request, while the source may be set to
SW2, 2, indicating switch 2, interface 2. A loop-free broadcast
tree may be built which includes emulated SW5, and thus the tree
indicates the shortest path to emulated SW7 302 (this may have been
performed earlier in the process than the receipt of the ARP
request). The ARP request may then be passed via the shortest path
to emulated switch SW7. However, edge switch SW5 310, recognizing
that the next switch is an emulated switch, may strip the
MAC-in-MAC header. One of the routers 306, 308 may receive the ARP
request and respond with an ARP reply. Here, it is assumed that
this would be router 308. Upon receiving the ARP reply, edge switch
SW5 310 may add a MAC-in-MAC header to arrive at the packet
depicted in FIG. 6. The destination address 600 of the MAC-in-MAC
header in the reply may be SW1. The source address 602 of the
MAC-in-MAC header of the reply may be emulated switch SW7. An
interface identification may also be included but such a value is
irrelevant anyway since the packet is not going to be used to
perform forwarding. Edge switch SW5 310 may then learn that router
308 is on its interface (e.g., interface 2). This information may
be synchronized with information on switches throughout the DCE
network, so that each switch knows that router 308 is on the
interface of edge switch SW5 310. The ARP reply may then flow
through switches 312, 304 to host A 300.
[0034] When host 300 then wishes to send normal traffic out through
the anycast hardware address corresponding to emulated switch SW7
302, SW2 304 may receive the traffic. It may then look up the
anycast hardware address in its table, finding that it is on
emulated switch SW7. It then may add the MAC-in-MAC header to the
traffic and forward it via the shortest path to emulated switch
SW7. Once again, edge switch 310 recognizes that switch SW7 is an
emulated switch and strips the MAC-in-MAC header off prior to
forwarding it on. By doing so, routers 306 and 308 have been load
balanced because a packet originating from host A 300 will be
transmitted through router 308 (using the shortest path) while a
packet originating from sever B 314 will be transmitted through
router 306. In cases where both paths are equal, a tie-breaking
mechanism may be used such as hashing based on the source address.
Additionally, as stated above, if one link goes down, the DCE
network is able to forward all packets to the other router until
such time as the link is restored.
[0035] FIG. 7 illustrates an example method for handling a hardware
address request, such as an ARP request or an IPv6 Neighbor
Solicitation, to a first router in an emulated switch of two or
more routers. This process may be performed at a layer 2 edge
switch in a network containing layer 2 switches. At 700, the
hardware address request may be received from a layer 2 switch.
This request may be an ARP request and may include a layer 2
network header (e.g., MAC-in-MAC header) that was added to the
request by another layer 2 switch (not necessarily the layer 2
switch from which the request was directly received). At 702, this
layer 2 network header may be stripped from the request. At 704,
the hardware address request may be forwarded to the first router.
It does not matter which router within the emulated switch is
designated as the first router. At 706, a hardware address reply
may be received from the router. This reply may be an ARP reply and
may include an anycast hardware address shared between each router
in the emulated switch. At 708, a layer 2 network header, such as a
MAC-in-MAC header, may be added to the hardware address reply. At
710, the hardware address reply may be forwarded to another layer 2
switch. This may or may not be the same layer 2 switch as in
700.
[0036] FIG. 8 illustrates an example method for handling a packet
received at a layer 2 edge switch from a router in an emulated
switch of two or more routers. At 800, the packet may be received.
The packet may be an ARP reply but it could also be ordinary
traffic. The packet may include an anycast hardware address shared
between each router in the emulated switch. At 802, the anycast
hardware address may be added to a table along with an
identification of the edge switch. This table may be periodically
synchronized with tables associated with other layer 2 switches in
the network. At 804, a layer 2 network header, such as a MAC-in-MAC
header, may be added to the packet. At 806, the packet may be
forwarded to another layer 2 switch in the network.
[0037] FIG. 9 illustrates an example method for handling a packet
from a host at an edge switch in a network containing layer 2
switches. At 900, the packet may be received. The packet may
include an anycast hardware address of an emulated switch
corresponding to a plurality of routers. At 902, a switch
identifier may be determined for the emulated switch using the
anycast hardware address. This may be determined by, for example,
looking up the anycast hardware address in a table to retrieve the
switch identifier. At 904, a header may be added to the packet, the
header including the switch identifier. This header may be a layer
2 network header, such as a MAC-in-MAC header. At 906, the packet
may be forwarded to another layer 2 switch along the shortest path
to the emulated switch. The shortest path may be determined by for
example, referencing a spanning tree created for the switches,
including the emulated switch. If there is a tie between two paths
such that the shortest path cannot be determined based on distance,
the tie may be broken by, for example, referencing a hash table
based upon the source address of the packet.
[0038] FIG. 10 illustrates an example method for handling a packet
from a host at an edge switch in a network containing layer 2
switches. At 1000, the packet may be received. The packet may
include a destination anycast hardware address of an emulated
switch corresponding to a plurality of routers. At 1002, a switch
identifier may be determined for the emulated switch using the
anycast hardware address. This may be determined by, for example,
looking up the anycast hardware address in a table to retrieve the
switch identifier. At 1004, a header may be added to the packet,
the header including the switch identifier. This header may be a
layer 2 network header, such as a MAC-in-MAC header. At 1006, a
shortest path to the emulated switch may be determined At 1008, it
may be determined if the shortest path includes a link that is
inoperative. If so, then at 1010, a new shortest path may be
selected that does not include a link that is inoperative. At 1012,
the packet may be forwarded to another layer 2 switch along a path
representing the shortest path to the emulated switch. The shortest
path may be determined by for example, referencing a spanning tree
created for the switches, including the emulated switch. If there
is a tie between two paths such that the shortest path cannot be
determined based on distance, the tie may be broken by, for
example, referencing a hash table based upon the source address of
the packet.
[0039] FIG. 11 illustrates an example apparatus for handling a
hardware address request to a first router in an emulated switch of
two or more routers. This apparatus may be a layer 2 edge switch or
a portion of a layer 2 edge switch (e.g., software). A hardware
address request receiver 1100 may receive the hardware address
request from a layer 2 switch. This request may be an ARP request
and may include a layer 2 network header (e.g., MAC-in-MAC header)
that was added to the request by another layer 2 switch (not
necessarily the layer 2 switch from which the request was directly
received). A layer 2 network header stripper 1102 coupled to the
hardware address request receiver 1100 may strip this layer 2
network header from the request. A hardware address request
forwarder 1104 coupled to the layer 2 network header stripper 1102
may forward the hardware address request to the first router. It
does not matter which router within the emulated switch is
designated as the first router. A hardware address reply receiver
1106 may receive a hardware address reply from the router. This
reply may be an ARP reply and may include an anycast hardware
address shared between each router in the emulated switch. A layer
2 network header adder 1108 coupled to the hardware address reply
receiver 1106 may add a layer 2 network header, such as a
MAC-in-MAC header, to the hardware address reply. A hardware
address reply forwarder 1110 coupled to the layer 2 network header
adder 1108 may forward the hardware address to another layer 2
switch. This may or may not be the same layer 2 switch as
before.
[0040] FIG. 12 illustrates an example apparatus for handling a
packet received at a layer 2 edge switch from a router in an
emulated switch of two or more routers. A packet receiver 1200 may
receive the packet. The packet may be an ARP reply but it could
also be ordinary traffic. The packet may include an anycast
hardware address shared between each router in the emulated switch.
An anycast hardware address table adder 1202 coupled to the packet
receiver 1200 may add the anycast hardware address request to a
table along with an identification of the edge switch. This table
may be periodically synchronized with tables associated with other
layer 2 switches in the network. A layer 2 network header adder
1204 coupled to the anycast hardware address table adder 1202 may
add a layer 2 network header, such as a MAC-in-MAC header, to the
packet. A packet forwarder 1206 coupled to the layer 2 network
header adder 1204 may forward the packet to a layer 2 switch in the
network.
[0041] FIG. 13 illustrates an example apparatus for handling a
packet from a host at an edge switch in a network containing layer
2 switches. A packet receiver 1300 may receive the packet. The
packet may include an anycast hardware address of an emulated
switch corresponding to a plurality of routers. A switch
identification unit 1302 coupled to the packet receiver 1300 may
determine a switch identifier for the emulated switch using the
anycast hardware address. This may be determined by, for example,
looking up the anycast hardware address in a table to retrieve the
switch identifier. A switch identifier header adder 1304 coupled to
the switch identification unit 1302 may add a header to the packet,
the header including the switch identifier. This header may be a
layer 2 network header, such as a MAC-in-MAC header. A shortest
path packet forwarder 1306 coupled to the switch identifier header
adder 1304 may forward the packet to another layer 2 switch along a
path representing the shortest path to the emulated switch. The
shortest path may be determined by for example, referencing a
spanning tree created for the switches, including the emulated
switch. If there is a tie between two paths such that the shortest
path cannot be determined based on distance, the tie may be broken
by, for example, referencing a hash table based upon the source
address of the packet.
[0042] FIG. 14 illustrates an example apparatus for handling a
packet from a host at an edge switch in a network containing layer
2 switches. A packet receiver 1400 may receive the packet. The
packet may include a destination anycast hardware address of an
emulated switch corresponding to a plurality of routers. A switch
identification unit 1402 coupled to the packet receiver 1400 may
determine a switch identifier for the emulated switch using the
anycast hardware address. This may be determined by, for example,
looking up the anycast hardware address in a table to retrieve the
switch identifier. A switch identifier header adder 1404 coupled to
the switch identification unit 1402 may add a header to the packet,
the header including the switch identifier. This header may be a
layer 2 network header, such as a MAC-in-MAC header. A shortest
path determiner 1406 coupled to the switch identifier header adder
may determine a shortest path to the emulated switch. A shortest
path inoperative link determiner 1408 coupled to the shortest path
determiner 1406 may determine if the shortest path includes a link
that is inoperative. If so, then a new shortest path determiner
1410 coupled to the shortest path inoperative link determiner may
select a new shortest path that does not include a link that is
inoperative. A shortest path packet forwarder 1412 coupled to the
shortest path inoperative link determiner 1408 and the new shortest
path determiner 1410 may forward the packet to another layer 2
switch via a path representing the shortest path to the emulated
switch. The shortest path may be determined by for example,
referencing a spanning tree created for the switches, including the
emulated switch. If there is a tie between two paths such that the
shortest path cannot be determined based on distance, the tie may
be broken by, for example, referencing a hash table based upon the
source address of the packet.
[0043] In each of these embodiments, various protocols may be used
(for example, DCE using the IS-IS protocol). Additionally, in each
of these embodiments, it is no longer necessary to run a hot
standby routing protocol.
[0044] FIG. 15 illustrates a simplified architecture of DCE switch
1500. DCE switch 1500 includes N line cards, each of which
characterized by and ingress side (or input) 1205 and an egress
side (or output) 1525. Line card ingress sides 1505 are connected
via switching fabric 1550, which includes a crossbar in this
example, to line card egress sides 1525. In this embodiment, one or
more of the processes described above is performed by one or more
of the line cards.
[0045] Although illustrative embodiments and applications of this
invention are shown and described herein, many variations and
modifications are possible which remain within the concept, scope,
and spirit of the invention, and these variations would become
clear to those of ordinary skill in the art after perusal of this
application. For example, it is possible that an edge switch is
connected to multiple routers within a single emulated switch.
Accordingly, the embodiments described are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalents of the appended claims.
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